This invention relates in general to a rack and pinion steering assembly, and more particularly relates to a seal assembly for use within the rack and pinion steering assembly.
A typical rack and pinion steering assembly has a housing containing a rack and a pinion. The rack has a longitudinally extending row of rack teeth in meshing engagement with helical gear teeth on the pinion. The opposite ends of the rack project outward from the housing and are connected with a steering linkage and a corresponding pair of steerable vehicle wheels. The pinion is connected with the vehicle steering wheel by an input shaft and a torsion bar. When a steering maneuver is being performed the pinion rotates and the rack moves longitudinally. The housing also contains a spring loaded yoke that presses the rack against the pinion to maintain the rack teeth in meshing engagement with the gear teeth on the pinion.
Typical power-assisted rack and pinion steering assemblies include a valve portion that uses hydraulic power to assist the steering operation of the vehicle. A valve assembly is formed within the valve portion and includes the input shaft, the torsion bar, a valve sleeve and a pinion gear. When the rack and pinion steering assembly is mounted in a vehicle, the input shaft is connected to a steering wheel. Rotation of the steering wheel results in rotation of the input shaft. The input shaft is fixed relative to the end of the torsion bar so that rotation of the input shaft results in rotation of the end of the torsion bar. Torsion of the torsion bar causes a valve core to move relative to a valve sleeve.
In a neutral position, hydraulic fluid flows from a source through passages in the valve sleeve. An equal amount of fluid is directed toward opposed passages in the valve sleeve. Since an equal amount of fluid is directed through each passage, the pressure within the system is balanced. When a steering operation is performed, the valve core is rotated relative to the valve sleeve and the valve assembly moves out of the neutral position, or is actuated, and fluid is directed toward a rack section. A piston divides the rack section into two chambers so that depending on which way the steering wheel is rotated, fluid can flow to either a left or right chamber to facilitate movement of the rack. A higher pressure in a first chamber relative to the pressure in the second chamber results in a differential pressure that causes the piston to move. When the piston moves, the rack moves and the steerable wheels are turned.
To prevent hydraulic fluid from flowing out of the chamber, it is necessary to seal the ends of the chamber through which the rack projects. It is also desirable to support the rack for axial movement within the chamber without losing the integrity of the seal. A bushing and seal assembly is typically used for this purpose. It is known to enclose the ends of the chamber with bellows attached to the housing to prevent the ingress of moisture, dirt, or other contaminant into the housing and bearing surfaces.